The invention generally relates to hydraulic cylinders, and more particularly, to high pressure seal assemblies for use on cylinders.
Equipment implementing hydraulic cylinders for mechanical movement, such as excavators and other heavy construction equipment, depend upon operators to manually move control levers to open and close hydraulic valves that direct pressurized fluid to hydraulic cylinders. For example, when the operator lifts a lift arm, the operator actually moves a lever associated with the lift arm causing a valve to release pressurized fluid to the lift arm cylinder. The use of levers to control hydraulic equipment depends upon manual dexterity and requires great skill. Improperly operated equipment poses a safety hazard and faulty operation of excavators, bucket loaders or like equipment may cause damage of overhead utility wires, underground wiring, water mains, and underground gas lines.
The operation of such hydraulic cylinders depends upon a position sensor such as a rotary potentiometer or other type of sensor such as those relying upon optical, conductive plastic or metal-in-glass technologies. It is a disadvantage of these sensors that they mount to the outside of the machinery, thereby exposing them to the environment. In the case of heavy equipment, this environment includes severe temperatures, excessive moisture, and air-borne particulate mater which may infect the sensor. In the case of optical, conductive plastic and metal-in-glass technologies, the sensors would rapidly degrade if used on construction equipment. Furthermore, some of these sensors use contacting components that are susceptible to wear, vibration and temperature. Thus, there is a demand for a low cost, long-life sensor operable in a harsh environment.
A sensor according to the present invention provides a precision signal utilizing a robust transducer. In one embodiment, the sensor mounts inside a hydraulic cylinder, away from the harsh environment, and provides a voltage or current signal indicative of the position of the piston. The sensor provides a connector, attached between a cylinder piston and a converting element, for sensing the displacement of the piston. The converting element converts the cylinder displacement to a proportional displacement of a translating member. A precision transducer senses the displacement of the translating member and provides an electrical output signal proportional to the piston movement or to the piston""s position.
The electrical conductors can be passed through the wall of the hydraulic cylinder via a high pressure seal assembly that provides an electrical path for the sensor located within the high pressure environment of the cylinder to an external connector that is in the ambient environment where some external electronic equipment recognizes the various signals from the sensor and interprets those signals to determine the position of the piston.